若阀件符号为A时，其工艺阀门叫（）。
A.疏水阀
B.止回阀
C.安全阀
D.闸阀
参考答案：C
To make our city more beautiful, rubbish ________ into the river. [ ]
A. needn't be thrown
B. mustn't be thrown
C.can't throw
D. may not throw
葡萄胎最重要的病理特征是绒毛间质水肿。
